The present invention relates to an electric tool, operated independently from the mains, which comprises an electric motor for operating the electric tool as well as a battery. In addition, the electric tool comprises a monitoring device for monitoring a monitoring operation-value limit, wherein the monitoring operation-value limit lies above an operation-value limit of the battery. Furthermore, the electric tool comprises an adjustable resistor component for varying the power output of the electric motor as well as an operation-value controller for setting at least one of the operation-values present at the electrical motor by means of pulse width modulation (PWM).
Furthermore, the present invention relates to a method for controlling an electric motor in an electric tool, operated independently from the mains, by means of a time-controlled monitoring of a monitoring operation-value limit by means of a monitoring device, wherein the monitoring operation-value limit lies above an operation-value limit of a battery.
Typically, hand-operated, battery-driven electric tools, such as drills, screwdrivers, saws, or similar, have various protection and shut-off functions, which serve to protect the individual systems within and also outside of the electric tool. These include for example the undervoltage lockout, which ensures that the respective electric tool is shut off when the supply voltage of a battery falls below a predefined limit. Turning off the electrical device serves to prevent drawing power up to almost complete depletion of the battery's capacity (risk of deep discharge), which can result in irreparable damage to the battery. Also the undervoltage lockout also serves to protect other systems, in particular the control electronics of the electric tool, from malfunctioning, damage, or destruction. The undervoltage lockout prevents the continued use of the electric tool until the battery again puts out a voltage lying at least above the supply voltage limit. Such an interruption in using an electric tool caused by the undervoltage lockout represents a substantial impairment for the user, since a shutoff due to an undervoltage is associated with a relatively long waiting period until one can continue using the electric tool.
Extreme environmental influences, particularly low temperatures, i.e., temperatures that lie well below a conventional room temperature of approx. 18° C., cause in some cases drastic output reductions in storage batteries. The reason is that in the cold, chemical processes proceed more slowly and the viscosity of the electrolytes used in Li cells increases considerably; at the same time, storage batteries and particularly lithium-ion storage batteries experience an increased internal resistance at low temperatures. However, the decrease in the providable output (voltage) of a battery results in the limit of the supply voltage being undershot even earlier when using the electric device. Particularly due to load peaks, which can occur during a temporary high output demand by the electric motor (e.g., for higher torque), the limit of the supply voltage can be quickly undershot. As a consequence of this, the undervoltage lockout intervenes in the controller of the electric motor and at least temporarily interrupts the output of the electric motor to prevent damage to the battery and the other systems. Users hereby repeatedly experience undesired interruptions when using the electric tool.
Due to the potential risk of deep discharges as well as the associated possible damage to a battery, one cannot forego continuous monitoring of the battery voltage or effective undervoltage lockout in an electric tool. On the other hand, the undervoltage lockout's continuous shutting off of the electric device, particularly at low ambient temperatures, results in inefficient working with the electric tool or prevents it entirely. In addition, the regular shutting off of the electric motor prevents the electric motor, and thus the electric device as well as the battery itself, from being able to heat themselves up, to thereby be able to avoid a temperature-caused shutoff by the undervoltage lockout.
Furthermore, there is the problem when the battery voltage suddenly increases again due to a load change on the electric motor. Such a load change can occur particularly because of a load reduction on the electric motor due to a decrease of the torque to be applied or because of an increase of the battery temperature due to intrinsic heating of the electric tool. In the case of load changes, the battery voltage increases again above the monitoring voltage limit, whereupon the controller assumes again that there is sufficient battery voltage and the PWM duty cycle of the voltage regulator for adjusting the operating voltage is derived again directly from the current position of the potentiometer. This elevated operating voltage again results directly in most cases in a drop in the battery voltage below the monitoring voltage limit and thus to a type of fluctuation behavior between the reduction of the operating voltage, or the PWM duty cycle of the voltage regulator, and the normal operating mode without such a reduction. Likewise, erratic changes of the battery voltage can cause rapid voltage drops that nevertheless result in the electric tool shutting off.
An object of the present invention consists in solving the problem described above and to this end providing a mains-independently operated electric tool as well as a method for controlling an electric motor in a mains-independently operated electric tool to ensure effective use of a battery for operating an electric tool.
The task is solved according to the invention by means of a mains-independently operated electric tool, which comprises an electric motor for operating the electric tool as well as a battery. In addition, the electric tool comprises a monitoring device for monitoring a monitoring operation-value limit, wherein the monitoring operation-value limit lies above an operation-value limit of the battery. Furthermore, the electric tool comprises an adjustable resistor component to vary the output delivered by the electric motor as well as an operation-value controller for setting at least one operation-value present at the electric motor by means of pulse width modulation (PWM).
According to the invention, a PWM duty cycle of the operation-value controller is established for setting the at least one operation-value, which corresponds to a first value or a second value, in which the first value can be derived from the current setting of the resistor component and the second value corresponds to the PWM duty cycle last used for setting the at least one operation-value plus an offset value, wherein for setting the at least one operation-value, the lower of the first or second value is selected for the PWM duty cycle if the at least one operation-value of the battery lies above the monitoring operation-value limit. One hereby prevents the at least one operation-value of a battery from dropping again rapidly below the operation-value limit of the battery, whereby a shutting off of the electric motor to protect the battery or other systems is avoided, and simultaneously one can continue using the electric tool. The operation-value may be a voltage value, for example. However, it is also possible that the operation-value pertains to the current strength or similar. Furthermore, it is also possible that the operation-value is the operating mode, i.e., the switched-on mode or the switched-off mode of the electric tool.
According to an embodiment of the present invention, the operation-value limit may be adjustable depending on a temperature value. The temperature value may be for example the temperature of the battery or the temperature of the electric device. However, it is also possible that the temperature value corresponds to the temperature of the battery and the temperature of the electric device. This means that the temperature value can be adjusted either only to the temperature of the battery or only to the temperature of the electric device without taking into account the temperature of the battery. Furthermore, it may also be possible that the temperature value stems from a combination of the temperature of the battery as well as the temperature of the electric device. In addition, it may also be possible that for the temperature value, the ambient temperature of the battery and/or the electric device are additionally or exclusively taken into account for setting the operation-value limit.
Depending on the respective temperature value, the operation-value limit may be set lower or higher. It is hereby provided that for a low temperature value, the operation-value limit is set lower, wherein however it shall be noted that the operation-value limit always lies below the monitoring operation-value limit. Accordingly, the operation-value limit is set higher for a low temperature value.
According to another embodiment, the offset value may correspond to a percentage of the PWM duty cycle last used for controlling the electric motor. In particular, the percentage may correspond to a value between 2% and 20% of the PWM duty cycle last used to control the electric motor. However, it is also possible that a higher or, equally, a lower offset value, depending on a temperature value, can be used. The temperature value may be for example the temperature of the battery or the temperature of the electric device. However, it is also possible that the temperature value corresponds to the temperature of the battery and the temperature of the electric device. This means that the temperature value can be adjusted either only to the temperature of the battery or only to the temperature of the electric device without taking into account the temperature of the battery. Furthermore, it may also be possible that the temperature value stems from a combination of the temperature of the battery as well as the temperature of the electric device. In addition, it may also be possible that for the temperature value, the ambient temperature of the battery and/or the electric device are additionally or exclusively taken into account for setting the operation-value limit.
To ensure regular monitoring of the voltage values of the battery, a time-controlled monitoring apparatus may be provided for the periodic monitoring of the at least one operation-value of the battery.
The time-controlled monitoring apparatus may be designed, according to an embodiment of the present invention, in such a manner that the at least one operation-value of the battery is monitored in time-based intervals. In particular, the time interval may correspond to a value between 1 ms and 100 ms. However, it is also possible that larger or smaller time intervals can be used to monitor the at least one operation-value of the battery depending on a temperature value. The temperature value may be for example the temperature of the battery or the temperature of the electric device. However, it is also possible that the temperature value corresponds to the temperature of the battery and the temperature of the electric device. This means that the temperature value can be adjusted either only to the temperature of the battery or only to the temperature of the electric device without taking into account the temperature of the battery. Furthermore, it may also be possible that the temperature value stems from a combination of the temperature of the battery as well as the temperature of the electric device. In addition, it may also be possible that for the temperature value, the ambient temperature of the battery and/or the electric device are additionally or exclusively taken into account for setting the operation-value limit.
According to another advantageous design of the present invention, it is also possible that the monitoring operation-value limit is realized by a monitoring voltage limit, the operation-value limit by an undervoltage limit, the operation-value controller by a voltage regulator, and the at least one operation-value by the operating voltage. One can hereby prevent the voltage of a battery from dropping again below the operation-value limit of the battery, whereby a shutting-off of the electric motor to protect the battery or other systems can be prevented and simultaneously one can continue using the electric tool.
In addition, the task is achieved according to the invention by a method for controlling an electric motor in a mains-independently operated electric tool by a time-controlled monitoring of a monitoring operation-value limit by means of a monitoring apparatus, wherein the monitoring operation-value limit lies above an operation-value limit of a battery.
According to the invention, the method comprises setting at least one operation-value of the electric motor by specifying a PWM duty cycle of an operation-value controller to the lower value of a first value or a second one, wherein the first value can be derived from the last setting of the resistor component and the second value corresponds to the PWM duty cycle, last used to set the at least one operation-value, plus an offset value, if the at least one operation-value of the battery lies above the monitoring operation-value limit.
One hereby prevents the at least one operation-value of a battery from dropping too quickly again below the operation-value limit for the battery, whereby a shutting-off of the electric motor to protect the battery or other systems can be prevented and simultaneously one can continue using the electric tool.
In addition, according to another design of the present invention, the ability to set the operation-value limit depending on a temperature value may be provided. The temperature value may be for example the temperature of the battery or the temperature of the electric device. However, it is also possible that the temperature value corresponds to the temperature of the battery and the temperature of the electric device. This means that the temperature value can be adjusted either only to the temperature of the battery or only to the temperature of the electric device without taking into account the temperature of the battery. Furthermore, it may also be possible that the temperature value stems from a combination of the temperature of the battery as well as the temperature of the electric device. In addition, it may also be possible that for the temperature value, the ambient temperature of the battery and/or the electric device are additionally or exclusively taken into account for setting the undervoltage limit.
Depending on the respective temperature value, the operation-value limit may be set lower or higher. It is hereby provided that for a low temperature value, the operation-value limit is set lower, wherein however it shall be noted that the operation-value limit always lies below the monitoring operation-value limit. Accordingly, the operation-value limit is set higher for a low temperature value.
According to another embodiment of the present invention, a setting of the offset value corresponding to a percentage of the PWM duty cycle last used to control the electric motor may be provided. In particular, the percentage may correspond to a value between 2% and 20% of the PWM duty cycle last used to control the electric motor. However, it is also possible that a higher or also lower offset value, dependent on a temperature value, can be used. The temperature value may be for example the temperature of the battery or the temperature of the electric device. However, it is also possible that the temperature value corresponds to the temperature of the battery and the temperature of the electric device. This means that the temperature value can be adjusted either only to the temperature of the battery or only to the temperature of the electric device without taking into account the temperature of the battery. Furthermore, it may also be possible that the temperature value stems from a combination of the temperature of the battery as well as the temperature of the electric device. In addition, it may also be possible that for the temperature value, the ambient temperature of the battery and/or the electric device are additionally or exclusively taken into account for setting the undervoltage limit.
Furthermore, according to another design of the present invention, an adjusting of the time-based monitoring of the monitoring operation-value limit can be provided in time-based intervals. In particular, the time interval may correspond to a value between 1 ms and 100 ms. However, it is also possible that larger or smaller time intervals can be used to monitor the at least one operation-value of the battery depending on a temperature value. The temperature value may be for example the temperature of the battery or the temperature of the electric device. However, it is also possible that the temperature value corresponds to the temperature of the battery and the temperature of the electric device. This means that the temperature value can be adjusted either only to the temperature of the battery or only to the temperature of the electric device without taking into account the temperature of the battery. Furthermore, it may also be possible that the temperature value stems from a combination of the temperature of the battery as well as the temperature of the electric device. In addition, it may also be possible that for the temperature value, the ambient temperature of the battery and/or the electric device are additionally or exclusively taken into account for setting the operation-value limit.
In addition, according to an advantageous design of the present invention, it is also possible that the monitoring operation-value limit is realized by a monitoring voltage limit, the operation-value limit by an undervoltage limit, the operation-value controller by a voltage regulator, and the at least one operation-value by the operating voltage. One can hereby prevent the voltage of a battery from dropping again below the operation-value limit of the battery, whereby a shutting-off of the electric motor to protect the battery or other systems can be prevented and simultaneously one can continue using the electric tool.
Additional advantages are revealed in the following drawing description. The drawing depicts an embodiment of the present invention. The drawing, the description, and the claims comprise numerous features in combination. A person skilled in the art will appropriately consider the features also on an individual basis and bring them together in other reasonable combinations.